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jsonbeautifiers
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Python Verified by running the parser on CPython 3.14.3.

Unterminated string starting at: line L column C (char N)

The parser found an opening quote and reached the end of the input without a matching close. Python points at the start of the string rather than the end of the file, because the start is the part you can act on.

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Input

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What actually causes it

Ranked by how often each one turns out to be the answer.

  1. 01 An unescaped quote inside the value

    The inner quote ends the string early and the rest of the document runs on inside a new one.

  2. 02 A trailing backslash escaping the closing quote

    A Windows directory path ending in a backslash does exactly this.

  3. 03 The file is truncated

    Cut off mid-value by a size limit, a dropped connection, or a partial write.

The same mistake in other runtimes

The underlying problem is identical; only the wording differs. If a colleague reports one of these, they are looking at the same thing you are.

JavaScript (V8) Unterminated string in JSON at position 8 (line 1 column 9)

Questions

The file looks complete when I open it. What now?
Check the byte count against what you expected, and check the last line. A file truncated at a buffer boundary often ends mid-word with no other clue.

Fix it now

Paste the payload into the tool above, or go straight to the one built for this job.

Find the open string